1. Field
The present invention relates generally to data communication, and more specifically to techniques for estimating the characteristics (e.g., amplitude and phase) of a communication link using pilot and non-pilot data.
2. Background
Wireless communication systems are widely deployed to provide various types of communication such as voice, packet data, and so on. These systems may be based on code division multiple access (CDMA), time division multiple access (TDMA), or some other modulation techniques. CDMA systems may provide certain advantages over other types of system, including increased system capacity.
For many wireless communication systems, a pilot is transmitted along with signaling and traffic data (e.g., voice and/or packet data) from a transmitter unit to a receiver unit. The pilot is typically a known data pattern that is processed and modulated in a known manner. Signaling and traffic data are also processed and modulated via respective schemes, combined with the processed pilot, and transmitted to the receiver unit. The transmitted pilot allows the receiver unit to estimate the communication link used to transmit signaling and traffic data.
At the receiver unit, a rake receiver is often used to recover the transmitted pilot, signaling, and traffic data. The transmitted signal may be received via multiple signal paths (or multipaths), and each received multipath may be processed by a respective finger processor of the rake receiver. Each finger processor processes the pilot in a complementary manner to derive a pilot reference having amplitude and phase determined by the characteristics of that multipath. The pilot reference is typically used to coherently demodulate the signaling and traffic data, which are transmitted along with the pilot and are similarly distorted by the propagation path. The pilot references for the received multipaths are also used to combine the demodulated multipaths to derive an improved estimate of the transmitted signaling and traffic data.
The quality of the pilot reference directly impacts the performance of the demodulation process, which in turn determines the performance of the communication system. A higher quality pilot reference may be obtained by transmitting the pilot from the transmitter unit at higher transmit power level. However, since the amount of available transmit power is limited, transmitting the pilot at a higher power level consumes more resources and decreases the amount of power available for signaling and traffic data.
There is therefore a need in the art for techniques capable of providing a higher quality pilot reference based on the transmitted pilot, signaling, and (possibly) traffic data.